Fixes robot modules not regenerating

- Also added a type check

code/modules/mob/living/silicon/robot/robot_modules.dm

@@ -34,8 +34,11 @@
 	if(!stacktypes || !stacktypes.len) return
 
 	for(var/T in stacktypes)
-		var/O = locate(T) in src.modules
-		var/obj/item/stack/S = O
+		var/obj/item/stack/S
+		for(var/obj/O in src.modules)
+			if(O.type == T)
+				S = O
+				continue
 
 		if(!S)
 			src.modules -= null
@@ -43,6 +46,9 @@
 			src.modules |= S
 			S.amount = 1
 
+		if(!istype(S))
+			continue
+
 		if(S && S.amount < stacktypes[T])
 			S.amount++